No x-over adjustments will fix the drastically too far apart distance of your mains. For future ref. in a v2.0 HT design I'd work on altering that.

You said the freq. response is pretty good? Is this from 1 meter maybe? I'm betting 'yes'.
You should measure at where you sit to get the real response you're hearing. No way the left and right mains are the same much less either being flat.

That left speakers esp. being right exactly in the very corner of the room is a pretty big flaw -even more so with the right speaker being far from a side wall. Both aiming directly forward.

If you could place some filler in those built in wall shelf sections where you elec. and RP are that should help too since there's probably a lot of sound bouncing around in there. I've heard the effect of those 'nooks' in several rooms -always messy.

I hope when you work with the Dynaudio drivers (very good drivers BTW) you build cabinets that can be placed far from the walls. In-walls aren't high end.
It's hard enough to distance the room effects from speakers, but impossible when you actually couple the speakers to the walls themselves.

The B-G ribbons have a poor high end, but otherwise very highly regarded.
In themselves they're dipoles not monopoles though.

Some companies that use them in cabinets making them monopoles and also add small spiral ribbon tweeters to the take over the very high range. Genesis is one I think. Most use them in their open dipole state.

I have Newfrom Research and thier 45" ribbon (actually three 15" ribbons in one solid heavy steel case) is actually a monopole design (a 'must' IMO), flat +/-1db from it's 1000Hz x-over to ~16,000Hz, and only down another 1db at ~20Khz (slow smooth roll off beyond that).

To have near perfect response in this ribbon, they can't play as low as the B-G's, but they're mated to dual Scan Speak 8545's carbonfiber/pulp cones. These are one of the best drivers in the world, and blend seamlessly (once broken in) to the ribbons.
See their use in the $10K range Wilson WATT, ProAc, Nova, Vienna Acoustics, etc...
Flat down to ~30Hz (due to one of the lowest res. freq. of any 6 1/2" driver).
Only a ~30 degree phase shift through the x-over too.

You can buy the ribbons alone from Newform and the drivers from Parts Express, but the Newform 'kits' are about the same price and you'll get everything at once.
There's better x-over designs than Newform uses though available online (Yahoo forum).

If you still wanted in-walls you could mount the ribbons to the edge of the TV notch corners, and mount the woofers in the wall area next to them. That would be a much better distance (~6-8' tops for the best imaging in pretty much all speakers), but I highly rec. you use an actual in room design and put up some wall treatments.

In that white room you could have some long white heavy curtians with a layer of very light translucent cloth (very pretty for high SAP factor -heh) at the first reflections points which would work great to dampen echoes and not look like a geeky 'audio tweak'.

Throw a blanket over your RP when you listen to music too. Big help in getting rid of that big plastic audio reflector that an RP screen is.

I have a nice looking one that's set w/ weights on top of my RP so I can just flip in up or down whenever I need to.

Good luck